Bragg grating sensing instrument using a tunable Fabry-Pérot filter to detect wavelength variations

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Abstract
A two-Bragg-grating sensing system, demodulated with the use of a tunable Fabry-Pérot filter to detect the associated wavelength variation has been developed. To show the practicality of the system, a low cost ELED (with an output of at ) was used as the light source, incorporating readily available Bragg gratings centred around this wavelength. The relevant parameters considered in designing such a system have been analysed and are discussed in detail. With the use of a digital Gaussian filter to limit the noise, under the same conditions, the repeatability obtained was close to the optimum level achievable (with the 12-bit A/D card used), and the repeatability of the Bragg wavelength, determined with individual data points being averaged over ten measurements was 7 pm, when the signal to noise ratio was as low as 30:1. Temperature and strain sensitivities of and have been demonstrated with such an instrument. The potential for achieving a higher repeatability of the measurement is discussed.